Although silicone rubber blocks and silicone rubber sheets obtained by curing silicone rubber compositions, as well as silicone rubber moldings such as silicone rubber-coated fabrics etc. produced by coating and curing silicone rubber compositions on the surface of base fabrics or other substrates have been used in the past in electrical insulating materials and diaphragms, sealant materials, air bag materials, materials for tents, materials for hoses, outdoor leisure sheets, in clothing-related applications, and in various other areas, the residual tackiness of the surfaces of such silicone rubber moldings, which persists even after vulcanization and curing, causes problems because moldings stick together and generate peeling defects during attempts to unfold folded items, etc., and, in the past, such said problems have been addressed mostly by dusting the surfaces with talc and other powders.
This method, however, makes the manufacturing process more complicated and gives rise to criticism from the standpoint of environmental hygiene-related problems caused by the dust, etc., and, in order to resolve such problems, methods have been proposed for reducing the tackiness of the surfaces of silicone rubber moldings by providing surface irregularities, such as mesh-like, crepe, and crinkle patterns, etc. Methods used to provide such irregularities include methods, where irregularities are transferred onto an uncured silicone rubber composition with the help of a film having irregularities on its surface or with the help of an embossing roll, whereupon the composition is cured (see Japanese Patent Application Publication (hereinafter referred as to “Kokai”) No. 2003-155360 and Kokai No. 2004-189982). However, if the uncured silicone rubber composition utilized in such methods is liquid, limitations related to the form of the silicone rubber composition preclude its use, etc. In addition, while there are methods, in which a crinkle pattern is transferred to a silicone rubber layer by forming a silicone rubber layer on top of a mold release sheet with a crinkle finish and then removing the release sheet (Kokai No. Hei 9-141783), the use of special mold release sheets presents a concern in terms of molding costs. In addition, there is a method, in which a crinkle pattern is transferred to a silicone rubber surface by molding silicone rubber in a metal mold with a crinkle finish on the interior surface of its cavity (Kokai No. Hei 10-177964). This method, however, is only applicable to molded articles and is not economically efficient because molds have to be changed if the crinkle pattern is modified.
Moreover, Kokai No. Hei 10-268679 proposes a method, in which fine surface irregularities are formed by molding a silicone rubber composition containing dispersed lumpy particles with an average particle size of 20-100 μm and then removing the lumpy particles from its surface. However, under this method, the physical properties of the silicone rubber molding and its adhesion to the substrate tend to deteriorate because of the added lumpy particles and efficiency problems arise due to the step required for the removal of the lumpy particles. A silicone rubber-based coating composition for air bags, which contains from 0.1 wt % to 50 wt % of a spherical powder with an average particle size of from 10 to 300 μm, has been proposed in Kokai No. 2000-303022 (corresponding to U.S. Pat. No. 6,420,037). However, to achieve a sufficient reduction in tackiness, a relatively large amount of such spherical powder has to be added because the spherical powder sinks into the rubber, and, depending on the intended use, the physical properties of the silicone rubber moldings and their adhesion to the substrate may turn out to be insufficient.
Furthermore, in the silicone rubber moldings with surface irregularities obtained by the above-described methods, once formed, the irregularities cannot be modified in shape and cannot be smoothed away.